1. Field of the Invention
This invention relates to an X-ray small angle scattering measuring apparatus for measuring scattered rays emitted from a sample in a small angle region. In particular, the present invention relates to an ultra-small angle X-ray scattering measuring apparatus that can suitably be employed to measure scattered rays within such an ultra-small angle region that the angle of 2θ-diffraction is defined as 2θ≦0.08°.
2. Description of the Related Art
The X-ray small angle scattering method is known as a technique of determining the sizes and the shapes of crystal particles in the inside of a substance by observing X-ray scattering in a small angle region of 2θ-diffraction angle, e.g. 0°≦2θ≦5°. Slit type X-ray small angle scattering measuring apparatuses have been known as apparatuses which realize the X-ray small angle scattering method. Some kinds of slit type X-ray small angle scattering measuring apparatuses have been known, such as an X-ray small angle scattering measuring apparatuses employing an optical system that has three slits and an X-ray small angle scattering measuring apparatuses employing a Kratky U-slit.
Japanese Patent Laid-Open Publication No. 2001-356197 discloses an exemplar 3-slit type X-ray small angle scattering measuring apparatus. The disclosed X-ray small angle scattering measuring apparatus is adapted to limit divergence (or spreading) of X-rays entering a sample by means of the first and second slits to form parallel X-rays and obtain scattered rays in a small angle region from a sample by irradiating the sample with the parallel X-rays. The third slit exerts the effect of eliminating scattered rays emanated from the first and second slits. An X-ray small angle scattering measuring apparatus that employs the Kratky U-slit can realize a resolution higher than the 3-slit type X-ray small angle scattering measuring apparatus by controlling divergence of X-rays by means of the Kratky U-slit that is a block-shaped member.
Meanwhile, there has been an increasing demand, or desire, for clearly capturing scattered rays in an ultra-small angle region (2θ≦0.08°) in order to analyze the aggregate structure of a higher order of molecules of a polymer material such as plastic and rubber. In principle, it may be possible to analyze such an aggregate structure to meet the demand by measuring X-ray small angle scattering by means of a 3-slit type X-ray small angle scattering measuring apparatus or an X-ray small angle scattering measuring apparatus employing the Kratky U-slit. In reality, however, it is not possible to meet the demand for analyzing such an aggregate structure by means of an X-ray small angle scattering measuring apparatus of either type. The reason is that it is difficult for both the 3-slit type and the Kratky U-slit type X-ray small angle scattering measuring apparatuses to narrow the divergence angle of X-rays entering a sample, while maintaining the intensity of the X-rays to a high level, so that it is not possible to clearly remove the background in an ultra-small angle region and hence capture scattered rays from the sample in the ultra-small angle region.
X-ray small angle scattering measuring apparatuses employing a Bonse-Hart optical system have been known as X-ray small angle scattering measuring apparatuses designed to obtain information on scattered rays in an ultra-small angle region. As shown in FIG. 12A of the accompanying drawings as an example, such a device has a structure in which a monochromator 101 formed by using a channel-cut crystal is arranged between a sample S and an X-ray source 102 and an analyzer 103 also formed by using a channel-cut crystal is arranged between the sample S and an X-ray detector 104.
In FIG. 12A, reference symbols X, Y and Z indicate three-dimensional directions. The Z-direction is the direction perpendicular to the plane of FIG. 12A. In a measuring operation, as the analyzer 103 is driven to rotate for scanning around the axial line X0 of the analyzer 103 itself (so-called 2θ-rotation), it is possible to observe the change in the intensity I of scattered rays that corresponds to the change of 2θ-angle as shown in FIG. 12B. The 2θ-direction is the direction of rotation around the axial line X0 that is perpendicular to the XY plane. The XY plane is a plane that includes the optical axis X1 of X-rays extending from the X-ray source 102 to the X-ray detector 104 and orthogonal relative to the axial line X0 of 2θ-rotation. The XY plane may also be referred to as equatorial plane. The direction perpendicular to the equatorial plane that extends in the Z-direction may be referred to as latitudinal direction.
In an ultra-small angle X-ray scattering measuring apparatus employing a Bonse-Hart optical system, a parallel X-ray beam is formed not by partly removing X-rays emitted from the X-ray source 102 by means of a slit or slits, but by causing X-rays to be diffracted (namely be reflected) by the channel-cut crystal 101. At this time, the channel-cut crystal 101 also performs monochromatization that converts an X-ray beam containing X-rays of different wavelengths to a monochromatic (e.g. Kα1) X-ray beam. Therefore, the aforesaid ultra-small angle X-ray scattering measuring apparatus may irradiate a sample with a parallel and monochromatic X-ray beam. Further, with use of the analyzer 103, the precise monochromatic X-ray beam is directed to the X-ray detector 104. Thus, the ultra-small angle X-ray scattering measuring apparatus employing a Bonse-Hart optical system has been said to be capable of measuring scattered rays generated by the sample S in an ultra-small angle region.
However, the inventor of the present invention conducted an experiment and found that it was not possible to accurately capture scattered rays from a sample in an ultra-small angle region even by using a Bonse-Hart optical system. The reason for this is that divergence (namely spreading) of X-rays can not be limited in the latitudinal direction that is perpendicular to the equatorial plane, while the resolution in intra-equatorial-plane directions can be maintained high, e.g., to about 0.002° because divergence (or spreading) of X-rays can be limited in the equatorial plane by means of a monochromator and an analyzer. Note that the equatorial plane means the plane in which the X-ray detector is driven to move for scanning in order to capture scattered rays from a sample, and further means the plane in which the analyzer crystal 103 is driven to rotate in 2θ-rotation. When divergence (spreading) of X-rays is not limited in the latitudinal direction, a smearing phenomenon arises resulting in failing to accurately capture the pattern of scattered rays emitted from a sample.
A smearing phenomenon may also be referred to as a blurring/staining phenomenon that can arise when a plurality of Debye rings that are formed due to scattered rays from a sample are found one on the other in the X-ray detection region of the X-ray detector and stains the Debye rings that have been actually captured and makes them unclear. Now, a smearing phenomenon will be described in greater detail below by referring to FIGS. 13A and 13B of the accompanying drawings.
A smearing phenomenon appears when the width of X-rays entering a sample is sufficiently broader than the Debye rings of scattered rays arising from the sample. FIG. 13A schematically illustrates how incident X-rays R0 enter the sample S to produce scattered rays R1. Scattered rays R1 include a plurality of Debye rings D that are found one on the other. The width W0 of the incident X-rays R0 is sufficiently broader than the Debye rings forming scattered rays R1.
In FIG. 13A reference symbols X, Y and Z depict a three-dimensional space. The X-ray detector is driven to rotate in a manner of a 2θ-rotation around the Z-axis to detect scattered rays R1. In other words, the XY plane is an equatorial plane and the Z-direction that is perpendicular to the XY plane is the latitudinal direction. FIG. 13A illustrates a phenomenon observed in an ultra-small angle region (e.g., 2θ≦0.08°). The width W0 is so small that it may be contained in the X-ray optical axis of a wide-angle diffractometer, which may be a powder X-ray diffractometer.
From the viewpoint of ideal observation, the detection region A0 of a zero-dimensional X-ray detector such as an SC (scintillation counter) is supposed to detect a single Debye ring. If such is the case, a scattering pattern (Gaussian distribution pattern) A that is attributable to a single Debye ring is detected in FIG. 13B. However, when scattered rays R1 include a plurality of Debye rings D that are found one on the other, the detection region A0 detects those large number of Debye rings so that a scattering pattern B as indicted by symbol B in FIG. 13B that is attributable to a plurality of Debye rings is detected. In other words, when a smearing phenomenon occurs, significant peak information that indicates the sizes and the shapes of crystal particles that are present in a sample is buried in the background that arises due to a large number of Debye rings produced according to a broad X-ray beam width and hence cannot be detected.
With a Bonse-Hart optical system as shown in FIG. 12A, divergence (spreading) of X-rays in intra-equatorial-plane directions (namely intra-XY-plane directions) may be controlled by means of monochromator crystals. Therefore, it may be safe to assume that the influence of a smearing phenomenon in intra-equatorial-plane directions does not adversely affect the results of observation. However, since divergence (spreading) of X-rays is not controlled in the latitudinal direction (Z-direction), the sample S is irradiated with X-rays having broad width in the latitudinal direction to probably give rise to a smearing phenomenon. Then, it may not be possible to accurately capture the pattern of scattered rays in an ultra-small angle region due to the smearing phenomenon.
In FIG. 12A, a technique of narrowing the X-ray beam width in the latitudinal direction (Z-direction) by means of a slit or slits may be conceivable, for the purpose of dissolving the smearing phenomenon in the latitudinal direction. It may appear that Debye rings overlapping with each other within an ultra-small angle region (2θ≦0.08°) are reduced in number by means of such a technique so that the pattern of scattered rays may be accurately captured. However, the intensity of X-rays is made too weak to make it no longer possible to accurately observe X-rays when a slit is employed to control the width of an X-ray beam.